1. Field of the Invention
The present invention relates to a running control apparatus for car use by which a profile of a road ahead of an own vehicle is predicted according to road map information composed of a collection of plurality of nodes and a running state of the own vehicle is controlled according to the result of the prediction.
2. Description of the Related Art
The above running control apparatus for car use has already been proposed in U.S. patent application Ser. No. 09/056,244 by the present applicant. This running control apparatus for car use operates as follows. As shown in FIG. 4, there are provided coordinates composed of a large number of nodes N.sub.N (N.sub.N =N.sub.0, N.sub.1, N.sub.2, N.sub.3 . . . ) which are set at predetermined intervals on a road so that they can be used as road map data. According to link length L.sub.N defined as a distance between nodes N.sub.N and N.sub.N+1 which are adjacent to each other and also according to crossing angle .theta..sub.N defined as an angle formed by one link N.sub.N-1 N.sub.N and another link N.sub.N N.sub.N+1 which is located ahead of link N.sub.N-1 N.sub.N, a passing state decision quantity (car turning quantity) .theta..sub.N /L.sub.N is computed. A passable speed of node N.sub.N computed according to the passing state decision quantity .theta..sub.N /L.sub.N is compared with a passage predicting speed at which the own vehicle passes through node N.sub.N, and when it is decided that it is difficult for the own vehicle to pass through node N.sub.N, a warning is given to a driver or an automatic speed reduction is conducted on the own vehicle. The above passing state decision quantity .theta..sub.N /L.sub.N corresponds to a change quantity in an azimuth angle of the vehicle with respect to a moving distance of the vehicle. When this value is high, it is indicated that the road is curved, and when this value is low, it is indicated that the road is straight.
In this connection, in a navigation system to which the above running control apparatus for car use is applied, a decision whether or not the own vehicle is actually running on a road, the route of which can precisely guide the own vehicle to the destination (this road is referred to as a designated road hereinafter), that is, a decision whether the own vehicle is on route or off route is conducted by a method of map matching in which a moving locus of the own vehicle is superimposed on a road profile. Accordingly, when the own vehicle is transferred from a state of off-route to a state of on-route, alternatively when the own vehicle is transferred from a state of on-route to a state of off-route, there is temporarily generated a section in which it is impossible to decide whether or not the own vehicle is running on the designated road. In this case, the following problems may be encountered. Although the own vehicle is in a state of off-route, it is mistakenly decided that the own vehicle is in a state of on-route, and a warning is given to a driver or an automatic speed reduction is conducted on the own vehicle according to a profile of the designated road, that is, there is a possibility that the driver feels a sense of incongruity.